Which soil types are prohibited as backfill in drainfield installations?

The identification of Class 1a soil as prohibited backfill in drainfield installations is based on the soil's physical characteristics and behavior when wet. Class 1a soils are generally fine-grained, which means they have a high clay content. These soils tend to retain water and do not allow for adequate drainage. This property can lead to poor aeration around the drainfield trenches and can cause saturated conditions that may hinder the treatment of effluent.

In contrast, other soil types, such as Class 2, Class 3, and Class 4, exhibit better drainage characteristics. They have properties that allow for the passage of water and gases, reducing the likelihood of creating a saturated environment around the drainfield. Therefore, selecting appropriate soils for backfill is essential to ensure the effective functioning of the drainfield system. Proper soil management helps maintain the efficacy of the on-site sewage treatment system and protects the surrounding environment from potential contamination.